Pillaring of trioctahedral micas and vermiculites

ABSTRACT

Pillared trioctahedral micas and/or vermiculites are prepared. The process includes a conditioning operation for the partial reduction of the layer charge through an accelerated weathering process, and also includes a pillaring operation.

FIELD OF THE INVENTION

The present invention is related to pillared trioctahedral-type naturalmicas and vermiculites, to a preparation method thereof, and to theirapplications.

BACKGROUND OF THE INVENTION TECHNICAL BACKGROUND OF THE INVENTION

Pillared interlayered smectites (PILCs) with a large variety of pillarshave been described in the scientific literature (journals, patents),among which the Al-pillared clays are the most documented ones. Similarmaterials with pillars based on other elements such as Zr, Cr, Ti, Si,Fe, Ga, Si, Ta, V, Mo, Nb, combinations of two or more of these elementsor combinations of one or several of those elements with others elementsnot mentioned above (as e.g. Ni, Cu, Co, etc.), rare-earth (La, Ce . . .)—containing pillars have been successfully prepared and reported in theliterature. Pillared clays containing two or more elements in thepillars are also named mixed pillared clays.

Pillared clays show interesting potentialities in catalysis, ascatalysts or supports to catalytic phase(s) or in admixture with othercatalysts or catalyst components (e.g. zeolites, metal oxides, etc.),especially as catalysts for e.g. hydrocarbons transformation. Pillaredmaterials also find potential interest as adsorbents and in otherdomains such as in gas separation processes; as scavengers for heavymetals (treatment of waste water); in SO₂ and NO_(x) abatement; inpurification of edible oil, cation selective composite membranes; assolid electrolytes; as host materials for (conducting) polymers; etc.

Trioctahedral micas

Trioctahedral micas refer to layered 2:1 sheet (or lamellar) silicatesin which the octahedral layer is sandwiched between two adjacenttetrahedral layers and mainly contains divalent cations with the resultsthat all the possible octahedral positions are occupied. They differfrom dioctahedral micas (muscovite-type), where ⅔ of the octahedralpositions are filled with mostly trivalent cations. The general formulaof the end-member phlogopite mineral is K₂Mg₆(Si₆Al₂)O₂₀(OH,F)4. Thestructural substitutions mainly occur in the octahedral layers but alsoin the tetrahedral ones and are responsible for the wide range ofchemical compositions of the trioctahedral micas. The high number ofsubstitutions is at the origin of the high net negative layer charge inmicas. Potassium is usually the dominant interlayer cation ensuringelectroneutrality of the layers. Trioctahedral micas may containsubstantial amounts of fluorine (replacing structural hydroxyls) whichconveys resistance to weathering, hardness and thermal resistance. Theprincipal cations in the octahedral layer of natural trioctahedral micasare Mg²⁺, Fe₂₊, Al³⁺ and Fe³⁺, with smaller proportions of Mn²⁺, Ti⁴⁺and Li⁺. Phlogopites refer to trioctahedral micas in which more than 70%of the occupied octahedral sites contain Mg²⁺, whereas biotites definethe micas where 20 to 60% of these sites are Mg²⁺ [Newman & Brown, inChemistry of Clays and Clay Minerals, A. C. D Newman (Ed.),Mineralogical Soc. 6, Longman, 1987, p. 75]. The potassium ions locatedbetween the unit layers just fit into hexagonal cavities (perforations)in the oxygen plane of the tetrahedral layers. Adjacent layers arestacked in such a way that the potassium ion is equidistant from 12oxygens, 6 of each tetahedral layer [R. E. Grim, Clay Mineralogy,McGraw-Hill, 1953, p.65]. In their original state, natural micas do notswell in the presence of water or polar solvents because the hydrationenergy of the interlayer potassium ions is insufficient to overcome theco-operative structural forces at the coherent edges of a cleavagesurface [Newman & Brown, Nature 223, 175, 1969].

The absence of swelling properties of natural micas makes it impossible,without modifying the mineral, to obtain pillared intercalated formsequivalent to those readily obtained with swelling clays (smectites) inwhich the clay sheets are separated from each other by pillars ofinorganic nature, which confer to these materials thermally resistantstructural and textural characteristics such as permanent elevatedspacings, high specific surface area and micropore volume, and surfaceproperties (acido-basic, redox).

Vermiculites

Vermiculites belong to a group of hydrated aluminium silicates. Theseminerals may be considered as “swelling trioctahedral micas” containingAl-for-Si substitutions in the tetrahedral layers (as in micas), andAl-, Fe-, and Ti-for-Mg substitutions in the octahedral layers. Becauseof both types of substitutions, the overall negative charge of thestructure results, as in micas, from an imbalance between the negativecharge of the tetrahedral layer and the excess positive charge of theoctahedral layer. As in micas and smectites, the excess negative chargeis counterbalanced by cations located in the region between adjacentsheets which ensure electroneutrality of the layers. Most often, theinterlayer cations are magnesium ions. The layer charge densities invermiculites are intermediate between those of micas and smectites.Unlike micas, vermiculites may swell and the layers may expand whenpolar molecules are introduced in the interlamellar region but thisswelling capability is much reduced compared with smectites. Theinterlayer charge balancing cations (magnesium ions) are exchangeable.

Vermiculites (and a fortiori micas) could not be intercalated with bulkypoly-hydroxy-aluminum species to form a pillared material exhibitingspacings of about 17-18 Å (gallery height of about 8 Å) as in pillaredsmectites, a failure which has been attributed to the high layer chargedensity of these minerals. Contacting vermiculite suspensions withAl₁₃-containing pillaring solutions led to expanded materials exhibitingonly about 14 Å spacings [references 1-7]. Taking advantage of the highspacings (27-28 Å) developed upon adsorption of long chain amines andalcohols to introduce Al pillars was unsuccessful [reference 5].Preliminary dealumination of vermiculite by treatment with an aqueoussolution of (NH₄)₂SiF₆ followed by the addition of the pillaringsolution did not result in materials with improved spacings [reference7]. A mixture of a pillared fraction of vermiculite (with 18 Å spacingstable at 500° C.) and of unpillared fraction was obtained uponcontacting with Al₁₃-containing solutions a suspension of vermiculitethat was previously treated with L-ornithine [reference 8]. However,repeated attempts to reproduce the method were unsuccessful.

State of the Art

The documents U.S. Pat Nos. 5,200,378 and 5,017,537 are concerned withthe pillaring of synthetic layered phosphates. Layered phosphates havenothing in common with natural micas. The intercalation is performedafter a previous intercalation of an amine (amide or dimethyl sulfoxide)in order to expand the interlayers. Attempts to pre-swell vermiculitewith a long chain amine or alcohol and to treat the expanded vermiculitewith a pillaring solution did not allow to obtain 18 Å Al-pillaredvermiculite.

The documents U.S. Pat. No. 5,340,657 and EP-0240359 deal with theAl-pillaring of synthetic sodium tetrasilicic fluor micas which havenothing in common with natural micas. The Na-TSF micas have onlyoctahedral substitutions (Li for Mg or Mg for Al), but no aluminium inthe tetrahedral layers. Natural micas have substitutions in both thetetrahedral (Al for Si) and octahedral (Al, Fe for Mg) layers. Na-TSFmicas are synthesized in a soda-containing medium (thus no interlayerpotassium as in natural micas). The presence of exchangeable Na in theinterlayers as charge neutralizing cations confers swelling properties.Natural micas have potassium ions between the layers and do not swell inpolar media. Na-TSF micas can be pillared when they are contacted withthe pillaring solution. Nothing like occurs when doing so with naturalmicas. This is the principal reason for the prerequisited conditioningoperation of the natural micas (aiming at the charge reduction ofvermiculites and micas and conversion to homoionic form of hydratedions). Synthetic Na-micas have, as hydrothermally synthetic layermaterials, very small particle sizes. Particles of the order of 0.1micron are preferred in the document EP-0240359 (p. 3, lines 8-10).

The document U.S. Pat. No. 4,510,257 describes a method which allows tointercalate three-dimensional silicon oxide pillars from organo-siliconderivatives in the clay interlayers. The material is then calcined todecompose the organic moiety. Vermiculite is mentioned (yet no exampleof successful Si-pillared material is provided).

The document WO98/00091 deals with the pillaring of synthetic layeredsilicate materials which have no octahedral layers and are thusdifferent from either synthetic sodium fluor tetrasilicic “micas” ornatural micas (as in our patent application), both of which havingoctahedral layers.

SUMMARY OF THE INVENTION

This invention describes a method for the obtention of pillaredtrioctahedral-type micas (PILMs) and vermiculites (PILVs) characterisedby thermally stable interlayer distances, high specific surface areasand micropore volumes, and acidic properties. These features are similarto those found for equivalent pillared interlayered materials obtainedfrom naturally occurring swelling clays, or smectites, (or theirhydrothermally synthesised analogues) such as montmorillonites(bentonites), beidellites, hectorites (fluorhectorite and laponite,synthetic analogues), saponites, nontronites, rectorites(interstratified montmorillonite-muscovite), Ni-SMM and SMM (theso-called synthetic expandable mica-montruorillonite) to quote some ofthe main ones used in the preparation of pillared interlayered clays(PILCs).

Pillaring is achieved after submitting the starting micas andvermiculites to a conditioning procedure consisting of chemical andthermal treatments which aim to reduce the layer charge density andreplace the charge balancing potassium ions located in the interlayersof the initial micas, or the magnesium ions in the case of vermiculites,by hydrated cations such as f.i. sodium ions. The charge-reducedcation-exchanged (Na⁺, Ca⁺², . . . ) forms of micas and vermiculites maybe converted to any other cationic form(s) by simple exchange of theinterlayer cations (f.i. Na⁺) by the desired element(s). Pillared micasand vermiculites are obtained by contacting Na-micas and Na-vermiculiteswith solutions containing the pillaring species, namely,polyoxohydroxymetal cations which intercalate between the layersaccording to a cation-exchange process, in a similar manner as for theobtention of pillared smectites. Successful insertion of Al-polymerisedspecies is not restricted to the sole Al element. Substitution of Al inthe pillaring solution by any one of the elements indicated below ormixtures thereof which have been successfully employed in thepreparation of pillared smectites, give rise to equivalent pillaredmicas and vermiculites, thus offering materials with a wide variety ofintercalated pillars and mixed pillars differing in the nature of thepillaring species and composition.

It is one object of the present invention that the same preparationprocedure may be equally applied to trioctahedral micas and vermiculitesand wastes thereof (as defined below) to obtain pillared materialsexhibiting the characteristic features of analogous materials preparedfrom smectites.

In accordance with the aforementioned objectives, it is a particularobject of the invention to find a new route to the pillaring oftrioctahedral micas and vermiculites with solutions containing Alhydroxy-polymeric species often referred to as AlO₄Al₁₂(OH)₂₄(H₂O)₁₂ ⁷⁺(in short, Al₁₃) with Keggin-like structure [reference 9]. Thisobjective is realized through the partial reduction of the layer chargedensity, which may be compared to an “accelerated weathering” process,and through the application of pillaring solutions in the form ofpartially hydrolysed Al solutions, the Al species in presence in thesesolutions having been identified [references 9-12].

It is a further object that this invention is not restricted to the solecase of aluminium as the metal element of the pillar since, as statedabove, substitution of Al in the pillaring solution by anyone of theelements Zr, Ti, Si, Cr, Fe, Ta, Nb, Ga etc. or combinations ofdifferent elements including lanthanides or mixtures thereof give riseto equivalent pillared micas and vermiculites.

Therefore, it is an object of the invention to give access via thesuccessful Al-pillaring of micas and vermiculites to the preparation ofmaterials with different types of pillar species (based, e.g., on Zr,Ti, Si, Cr, Fe, Ta, Nb, Ga, etc, or combinations of different elements,including lanthanides) with possible uses in various catalytic reactionsand other application areas.

Further, the greater intrinsic structural stability of micas andvermiculites compared with smectites is of considerable interest inachieving pillared materials which possess improved resistance tothermal treatments, a weakness shared by all smectite-based pillaredmaterials.

Another interest of the method is the possibility to use micas andvermiculites with various particle sizes.

Other objects of the invention include post-exchange and/or impregnationof the pillared materials, improvement of the acidic properties, use influidised bed applications.

Further details will appear in the claims and in the descriptionhereafter of preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents nitrogen sorption isotherms of the starting mica (Mi),of homoionic Na-exchanged mica (M4) and of Al-pillared mica calcined at500° C. (M5-500), 700° C. (M5-700) and 800° C. (M5-800). Outgassing at200° C. for 6 h.

FIG. 2 represents ²⁷Al MAS-NMR spectra of the starting mica (Mi) and ofsamples collected at step 1 (M1), at step 2 (M2), at step 4 (M4) andafter Al-pillaring (M5).

FIG. 3 represents nitrogen sorption isotherms of starting Palaboravermiculite (Pi), after sodium saturation (P4-Na), and of Al-pillaredvermiculite calcined at 400° C. (P5-400) and 700° C. (P5-700).Outgassing at 200° C. for 6 h.

FIG. 4 represents X-ray diffraction patterns of Al-pillared Palaboravermiculite (P5) after beating at different temperatures.

FIG. 5 represents nitrogen sorption isotherms of the startingpre-calcined vermiculite (Vi-500), after sodium exchange (V4-500), andof Al-pillared vermiculite calcined at 500° C. (V5-500) and 600° C.(V5-600).

FIG. 6 represents X-ray diffraction pattern of Al-pillared precalcinedvermiculite after heating at 500° C. (V5-500), 600° C. (V5-600), and700° C. (V5-700).

FIG. 7A represents hydroconversion of octane on Al-pillared micas:topcurves: variation of total conversion (C), of the yields of C8 isomers(Iso) and of the cracked products (Cr) versus reaction temperature.

FIG. 7B represents variation of the selectivity to C8 isomers vs. octaneconversion. Sample ZB25: reference zeolite beta.

FIG. 8A represents hydroconversion of octane on Al-pillaredvermiculites:top curves: variation of total conversion (C), of theyields of C8 isomers (Iso) and of the cracked products (Cr) versusreaction temperature.

FIG. 8B represents variation of the selectivity to C8 isomers vs. octaneconversion. Sample ZB25: reference zeolite beta.

FIG. 9 represents hydroconversion of octane on Al-pillared vermiculite(1S044), on modified Al-pillared vermiculite (3S044*), Al-pillaredsaponite (Al(ACH)PSY), and reference H-Beta zeolite (ZB25).

FIG. 10 represents reduction of NOx: variation of the conversion ofNO_(x) to N2 vs reaction temperature on Cu-ZSM-5 zeolite andCu-exchanged Al-pillared mica.

DETAILED DESCRIPTION OF THE INVENTION

General Description of the Pillaring Procedure

Al-pillared micas and vermiculites exhibiting stable spacings (18 Å andmore for room temperature dried samples) are obtained after:

i) a conditioning step which brings about a reduction of the layercharge density of the minerals and allows to convert the minerals infully exchanged monoionic forms and

ii) a pillaring step consisting of contacting the cation-exchangedminerals (monoionic forms) with the pillaring solution following anymethod known from the literature.

Efficient pillaring is achieved provided that the conditioning treatmentis properly carried out. Adequate conditioning can be controlled bycharacterising the solids at the different intermediate steps by use ofsuitable techniques and methods (e.g. X-ray diffraction, nitrogensorption isotherms etc.). These controls may require washing and dryingoperations which are superfluous in the continuous preparationprocedure.

In the “standard method”, the conditioning step of micas andvermiculites consists of four consecutive operations, prior to thepillaring operation itself. These two aspects will be discussedseparately.

Conditioning of the Starting Mica and Vermiculite

The conditioning treatment consists principally of the reduction of thelayer charge density of the starting minerals and the replacement of theinterlayer potassium ions in the initial mica, and of the magnesium ionsand other cations in the case of vermiculites, by hydrated cations (e.g.sodium ions). Conditioning is achieved through the following sequence oftreatments: the mineral is first treated with diluted mineral acid,preferably nitric acid. The solid is washed free of excess acid anddissolution products and then calcined at 500-650° C. Thereafter, thesolid is preferably leached with a diluted (mineral) acid, andpreferably with a complexing (chelating) organic acid. After eliminationof the excess complexing agent (or acid) and dissolution debris, thesolid is converted to the monoionic form by an usual ion-exchangetreatment with a solution of a soluble salt (e.g. of sodium), and washedfree from excess salt.

At this stage, the mineral is ready for the pillaring operation. Thissequence of treatments is similarly applied to micas and vermiculites(as well as to “wastes” thereof, as defined below). The exact conditionsof acid concentration and treatment duration, however, may differsomewhat for a mica and for a vermiculite as it will be illustrated inthe following examples.

Pillaring Operation

The monoionic forms of micas and vermiculites (Na⁺, Ca⁺², . . . ) arecontacted with a solution containing the pillaring species (thepillaring solution). The pillar precursors are introduced in theinterlayer space via an exchange process between the charge balancingcations of the minerals obtained at the end of the conditioningoperation and the positively charged species present in the pillaringsolution. Any known method used for the preparation of pillaredsmectites may be applied.

Detailed Description of the Conditioning Treatment

Step 1.—Nitric Acid Treatment

The starting phlogopite or vermiculite was leached with nitric acidsolution for 4 hours at 95° C. under stirring, using a concentration ofsolids between 4 and 20 wt %, typically 10 wt %. The ratio [mol ofnitric acid/mass of phlogopite] was included between 0.007 and 0.011 molg⁻¹, typically 0.008 mol g⁻¹. The concentration of the acid solutionranged between 0.29 M and 1.44 M, typically 0.78 M.

Step 2.—Thermal Treatment

The sample obtained at step 1 was calcined at 500-700° C., typically at600° C. for 4 hours under static air.

Step 3.—Treatment with Complexing Agents (Typically Oxalic Acid)

The treatment with a complexing agent mainly aims to remove the speciesdissolved from the structure in the preceding steps, which are partlypresent in the interlayers. The conditions were as follows:

Concentration of solids:

between 2.6 and 10 wt %, typically 10 wt %

Concentration of the completing acid solution:

between 0.06 M and 0.24 M, typically 0.12 M for 10 wt % of solid

Duration of the treatment:

micas: between 2.0 and 4 hours, typically 2.5 h

vermiculites : between 0.5 and 2 hours, typically 1 h

Temperature of treatment:

between 80 and 95° C., typically 80° C.

Alternative (Step-3) treatments:

Citric Acid

Sample obtained at step 2 was leached with a 0.5 M citric acid solution(pH 2.1) at 80° C. for 4 hours.

Concentration of solids between 1.7 and 4 wt %, typically 4 wt %.

Acetic Acid

Sample obtained at step 2 was leached with 0.005 mol acetic acid pergram of clay at 80° C. for 3 hours. Concentration of solids of 7.6 wt %.

Hydrochloric Acid

Sample obtained at step 2 was leached with 0.0002 mol hydrochloric acidpeer grain solid at 80° C. for 3 hours. Concentration of solids of 7.6wt %.

Step 4.—Sodium Exchange (*)

Concentration of the NaCl solution:

between 1 M and 3 M, typically 1 M.

Concentration of solids:

between 0.35 and 6.4 wt %, typically 2 wt %.

Number of exchange operations:

between 4 and 6, typically 5 for 12 hours each.

Temperature of exchange:

95° C.

At the end of this step, the exchange sites are occupied by sodium ions.Other cationic forms may be obtained by further exchange of the Na-formswith solution(s) of the desired element(s).

(*) Notes:

Any known cation exchange method may equally be used.

Any other salt of hydrated cations instead of a Na salt, and differentconcentrations of the exchange solution and exchange times may be used.

PREFERRED EMBODIMENTS OF THE INVENTION

1. Pillaring of micas

Starting phlogopite

The starting phlogopite-type mica (Siilinjaeervi deposit, Finland) was amicronized grade (particle size: 90% smaller than 40 microns, 50%smaller than 20 microns). Minor amounts of calcite and apatite wereidentified by X-ray diffraction.

The chemical analysis (by I.C.P.S.) was as follows (in wt % on the basisof samples calcined at 1000° C.).

SiO₂ Al₂O₃ MgO Fe₂O₃ K₂O CaO, NaO, TiO₂, P₂O₅ 41.05 9.71 23.73 7.93 9.50<6.83

Batch 1 Batch 2 Conditioning The conditioning operation follows thesteps as described heretofore. The exact operating conditions to preparetwo batches of Al-pillared micas are given hereafter Step 1 Conc. HNO₃(M) 0.72 0.78 Duration (in h) 4 4 Temperature (° C.) 95 95 Conc. solids(wt %) 10 10 mole H⁺ g⁻¹ solid 0.007 0.008 The resulting solid will benoted as M₁ Step 2 Calcination at 600-650° C. 4 h 4 h The resultingsolid will be noted as M₂ Step 3 Conc. oxalic acid sol. (M) 0.06 0.12Duration (in h) 3 2.5 Temperature (° C.) 80 80 Conc. of solid (wt %) 410 Mole H⁺ g⁻¹ solid 0.0015 0.0012 The resulting solid will be noted asM₃ Step 4 Conc. NaCl solution (M) 1 3 Number of renewals 5 × 2 h 5 × 12h Temperature (° C.) 95 95 Conc. of solids (wt %) 1.6 5 The resultingsolid will be noted as M₄ Pillaring procedure Step 5 Pillaring solution:OH/Al molar ratio: 2.4 2.4 inrnol Al g⁻¹ solid 24 24 Contact time (in h)4 4 Temperature (° C.) 80 80 The resulting solid will be noted as M₅,the pillaring operating step 5 is described below.

Step 5.—Pillaring Operation

The Na-exchanged mica M₄ was dispersed in water (1 wt % of solid), andstirred for 24 h (avoided in continuous process). Pillaring was doneaccording to existing procedures, as e.g. by slow addition of thepillaring solution to the mineral dispersion under stirring while thetemperature was increased to 80° C. (not indispensable). The volume ofthe Al₁₃ solution (pillaring solution) was adjusted in order to supply asufficient amount of the pillaring element (12 to 36 mmol Al per gram ofmica, typically 24 mmol g⁻¹).

The contact between the pillaring solution and the solid was maintainedfor 4 hours after the end of the addition, at 80° C. (not indispensable)under continuous stirring. The solution was eliminated by centrifugationand the sample was washed until the conductivity was reduced to 0.5 μScm⁻¹1 g⁻¹ (sample M₅). Sample M₅ was dried at 60° C. and calcined at thedesired temperature for characterization purposes.

Two different Al₁₃ sources (pillaring solutions) have been used: a base(e.g. NaOH) hydrolysed Al solution (e.g. AlCl₃), and a commercialsolution of Al-chlorhydrol (from Reheis Chem. Co., Ireland).

a) Pillaring with base hydrolysed Al solution (Typical pillaringsolution)

The pillaring solution was prepared (as in previous works [references12-14]) by slow addition of a 0.2 M NaOH solution to a 0.2 M solution ofAlCl₃, under stirring at 80° C. The required volume of base was added toreach an OH/Al molar ratio of 2.4. The Al concentration in the finalsolution was 0.06 M. The solution was aged at room temperature for atleast 24 h (not indispensable). It has been established that insolutions with this molar ratio, about 70-80% of the total aluminiumions are present as ‘Al₁₃ ⁷⁺’ oligocations [references 10, 11-14].

Notes:

OH/Al molar ratio is not limited to 2.4 as in the example.

Al concentration of the pillaring solution is not limited to 0.06 M

b) Pillaring with commercial Al-chlorhydrol (Reheis Chemical Company,Dublin).

Al-chlorhydrol (or commercial equivalents with trade name PAX and OCAL)is formed by the reaction of metal aluminium with aqueous AlCl₃. Thesesolutions also contain oligomers larger than Al₁₃ ⁷⁺ [reference 15]. Theanalysis of the starting Al-chlorhydrol (50% aluminium chlorhydratesolution) given by the supplier was as follows:

pH of 30% wt % Al₂O₃ wt % Cl⁻ Al:Cl atomic ratio Fe (ppm) wt/wt sol.23.7 8.25 1.96:1 46 4.30

The commercial solution was diluted to 0.1 M in Al and heated at 60° C.for 2 h immediately before use.

Notes:

Chlorhydrol may be used either undiluted or at any dilution. Dilution ishowever preferred.

Heating and ageing of the chlorhydrol solution are not indispensable.

In the following, “standard method” will refer to the complete sequenceof operations described above.

For characterisation purposes, the solids were recovered at the end ofthe different steps described below, washed when necessary and dried(superfluous in a continuous preparation procedure).

Characterisation of Intermediates

X-ray Diffraction Data

The spacings corresponding to the (001) reflection were determined fromX-ray diffraction patterns recorded with a Philips type PW 1130-90instrument (CoKα radiation, Fe-filtered) or a Siemens D-5000diffractometer (CuKα radiation, Ni-filtered). The scanning rate was 1°2θ min⁻¹. The spacings of intermediates are given in Table 1.

Sample M₁ (treated with nitric acid, washed and dried at 60° C.):

Three peaks appeared in the low angle region, one with spacing of 10.1 Å(starting phlogopite), and two new peaks at d=25 Å (absent in thestarting mica) and at 11.6 Å. After calcination at 500° C., only thepeak at 10.1 Å remained.

Sample M₂:

After calcination of M₁ at 600° C., only one peak remained at 10 Å.

Sample M₃:

Spacing analogous to that of M₂

Sample M₄:

Suitable Na-exchange was characterised by the expansion of the basalspacing to 12.2 Å at 60° C. (another peak with d=14.5 Å was observed inhigher humidity conditions). Na-exchange was confirmed by thecontraction of the basal spacing to 9.7 Å after heating at 500° C.

TABLE 1 XRD data: interplanar distances (in Å) Sample At roomtemperature At 500° C. M_(i) 10.1 10.1 M₁ 25, 11.7-11.5, 10.1 10.0 M₂10.0-10.15 — M₃ 10.1-10.25  10.05 M₄ 12.2, (14.5)  9.7 M₅ 18.5,(14.1-13.8)* 18.3-17.7 *: very weak intensity

Textural Characteristics

The surface areas (S_(BET)) were obtained by applying the BET treatmentto the nitrogen sorption isotherms measured at 77K (ASAP 2000Sorptometer, from Micromeritics) in the domain of relative pressures of0.05-0.25, on samples previously outgassed for 6 h at 200° C. The totalpore volumes (Vo) were established from the amount of nitrogen adsorbedat a relative pressure of 0.985, and the micropore volumes (Vμ) werecalculated by the ‘t-plot’ method [reference 16].

The experimental values are given in Table 2. The Na-exchanged sample(M₄) showed almost no microporosity, and a small increment of thesurface area and the total pore volume with respect to the startingmineral (M_(i)).

TABLE 2 Textural characteristics of samples calcined at 500° C.. BETspecific surface area (S_(BET)), total pore volume (V₀) and microporevolume (V_(μ), t-plot method). S_(BET) V₀ V_(μ) Sample m²g⁻¹) (cm³ g⁻¹)(cm³ g⁻¹) M_(i) 2 0.010 0.000 M₄ 28 0.067 0.000

An illustration of the complete N₂ isotherms of M_(i) and M₄ (outgassedat 200° C.) is shown in FIG. 1.

During the conditioning step, the particle size (measured with a CoulterLS130 apparatus) was almost unchanged in the medium and small size partof the distribution curve. A diminution of the size of the largerfraction was noticed, as shown in Table 3.

TABLE 3 Particle size analysis (0.1 μm-900 μm) Size (μm) Size (μm) Size(μm) Sample Mode (μm) 90%< 50%< 10%< M_(i) 67 277 59 17 M₄ 61 110 50 16

Other Characteristics

The cation exchange capacity (CEC) of M₄, determined by micro-Kjeldahlanalysis on an ammonium-exchanged sample, was 1.46 meq g⁻¹.

The ²⁷Al MAS-NMR spectrum of the starting mica (Mi in FIG. 2) (recordedwith a Bruker 400 MSL spectrometer; magnetic field of 9.4 T; pulselength of 0.6 μs; tipping angle of 10°; recycle delay of 0.1 s; spinningrate of the 4 mm diameter rotor: 12 kHz; number of scans: 3000) showed asignal at 63 ppm, characteristic of tetrahedral aluminium. After acidleaching (spectrum M1), there is a decrease of the signal at 63 ppm anda new signal appears at around 0-3 ppm, indicating that part of thetetrahedral Al has been converted to extraframework octahedral Al. Thesignals at 190 ppm and −60 ppm are side bands associated to the mainsignal at 63 ppm. After carrying out step 2 (spectrum M2), the signal at0-3 ppm is much reduced and slightly shifted to 10 ppm. It has almosttotally disappeared after the sodium exchange (spectrum M4). Thespectrum of the Al-pillared mica (M5) exhibits an intense signal atabout 0 ppm, typical of octahedral Al of the pillars. The two signals atabout 140 and −120 ppm are side bands associated with that at 0 ppm.

Characterization of Al-pillared micas

Sample M₅:

After treatment with the pillaring solution, intercalation of the Al₁₃species was evidenced by the expansion of the spacing to 18.7-18.5 Å. Aminor fraction of the mica was intercalated with smaller aluminiumspecies (mainly monomeric aluminium), characterised by a diffractionpeak at 14.1-13.7 Å.

Heating M₅ at 500° C. resulted in a limited contraction due todehydration-dehydroxylation of the pillar precursor (Keggin-type cation)to the corresponding pillar oxide. This contraction was shown by a smallshift of the 001 reflection from 18.5 Å to 18.3-17.7 Å, depending on thecalcination conditions, while the minor fraction intercalated withmonomeric species collapsed to 10.5 Å. These changes are summarized inTable 1.

Thermal stability, textural and structural characteristics (Al-pillaredmicas)

The DTG curve (obtained with a Setaram TG-DTA 92 thermobalance indynamic air atmosphere and heating rate of 10° C. min⁻¹) showed thatadsorbed water is removed at 150° C. A continuous weight loss occurredbetween 150 and 500° C. associated with the dehydroxylation of the OHligands of the aluminium pillars. Dehydroxylation of the mica structureoccurred at 800-850° C. The total weight loss (60-1000° C.) was 22.2%.

The textural characteristics established from the nitrogen sorptionisotherms are given in Table 4. The micropore volumes of the pillaredmicas were determined according to a method described in [reference 17].

The specific surface areas and the micropore volumes remain nearlyconstant after calcination up to 600° C. and keep high values even at700° C. A noticeable decrease of the surface area and microporous volumeis observed after calcination at 800° C. At 850° C. and above, thestructural identity of the pillared material is lost.

TABLE 4 Textural characteristics of pillared samples after calcination.(heating rate: 1° C. min⁻¹ with a plateau of 2 h at the finaltemperature; outgassing at 200° C. under 10⁻⁴ Torr) S_(BET) V₀ V_(μ)Sample (m² g⁻¹) (cm³ g⁻¹) (cm₃ g⁻¹) M₅-RT (batch 2) 356 0.220 0.129M₅-RT (batch 1) 351 0.250 0.123 M₅-400 (batch 2) 339 0.201 0.114 M₅-500(batch 1) 365 0.268 0.119 M₅-600 (batch 2) 339 0.201 0.114 M₅-700(batch 1) 283 0.153 0.094 M₅-800 (batch 1) 145 0.073 0.036

The complete N₂ adsorption-desorption isotherms of Al-pillaredphlogopite established after calcination at increasing temperatures areshown in FIG. 1 (M₅-500, M₅-700 and M₅-800).

The structural changes follow a similar tendency, namely, a relativelyslight diminution of the basal spacing after calcination at 400-600° C.But even at 800° C., the spacing remains quite high (see Table 5).

TABLE 5 Basal spacings (in Å) of M₅ after calcination for 2 h atincreasing temperatures (heating rate: 1° C. min⁻¹; plateau of 2 h atthe final temperature). T(° C.) 60 400 500 600 700 800 850 d₀₀₁ 18.718.3 17.7 17.4 16.2 16.0 12.7

The limit of the thermal stability was 840° C. (from DTA curve).

The acid content of Al-pillared phlogopite M₅ calcined at 500° C.(determined by adsorption of ammonia at 100° C. followed bytemperature-programmed desorption (TPD) of ammonia between 100 and 550°C.) was 0.29 meq g⁻¹.

Intercalation of Al₁₃ was confirmed by ²⁷Al MAS NMR spectroscopy. Thespectrum showed an increase of the signal at 63 ppm corresponding tostructural Al and to Al of the pillars, both in fourfold coordination,and a new signal at 3-4 ppm characterizing Al in octahedral coordinationoriginating from the pillars.

This is illustrated in FIG. 2 which compares the spectra obtained forthe starting mica (1), after Na-exchange (2), and after pillaring (3).The signals showing up above 100 ppm and below −20 ppm are side bands.

Variation of Some Preparation Parameters

Table 6 compiles the textural characteristics, namely the specificsurface areas (S_(BET)), the micropore volumes [method of reference 17](V_(μ)), and the total pore volumes (Vo) of M₅ solids in relation withthe conditions employed at each step.

All these pillared samples calcined at 500° C. showed basal spacingsbetween 17.4 Å to 18 Å.

TABLE 6 Textural parameters of selected samples (not typical conditions)S_(BET) V_(μ) V₀ Sample step 1 step 2 step 3 step 4 step 5 m² g⁻¹ cc g⁻¹cc g⁻¹ M₅-500 0.29 500 citric 6 × 1M lab-12 228 0.086 0.147 M₅-600 0.29500 citric 6 × 1M lab-12 222 0.073 0.146 M₅-700 0.29 500 citric 6 × 1Mlab-12 218 0.074 0.137 M₅-500 0.29 500 ox 5 × 1M lab-12 287 0.083 0.165M₅-500 1.44 500 ox′ 5 × 1M lab-24 261 0.097 0.191 M₅-700 1.44 500 ox′ 5× 1M lab-24 237 0.080 0.181 M₅-500 1.44 500 ox′ 4 × 1M lab-12 261 0.0890.193 M₅-500 1.44 500 ox′ 4 × 3M lab-12 237 0.079 0.163 M₅-500 0.72 500ox″ 5 × 1M lab-12 279 0.105 0.186 M₅-500 0.72 h500 ox″ 5 × 1M lab-12 2340.086 0.155 M₅-200 0.29 500 ox 5 × 1M lab-36 310 0.115 0.210 M₅-500 0.29500 ox 5 × 1M lab-36 264 0.094 0.193 M₅-600 0.29 500 ox 5 × 1M lab-36267 0.083 0.200 M₅-400/1 0.78 500 ox′ 3 × 3M Chlr-24 196 0.025 0.153

Step 1

Column entitled “step 1” gives the molar concentration (M) of the nitricacid solution.

The concentration of solids was 3 wt % for 0.29 M nitric acid; 10 wt %for 0.72 M and 0.78 M; and 20 wt % for 1.44 M (constant mol H⁺ g⁻¹solid=0.007).

Step 2

Column “step 2” shows the heating temperature; h meaning no drying priorto thermal treatment.

Step 3

Column “step 3” gives a code related to the nature of the complexingsolution, time and temperature used. The meaning of the code is thefollowing: ox: 0.06 M oxalic acid, 4 h, 80° C.; ox′: 0.12 M oxalic acid,3 h, 80° C.; ox″: 0.06 M oxalic acid, 3 h, 95° C.

Step 4

This column refers to the number of ion exchange operations performed(renewals of the exchange solution); xM refers to the molarity of theNaCl solution.

Step 5

Column “step 5” indicates the type of pillaring solution:lab: preparedby base-hydrolysis of AlCl₃ solution (OH/Al=2.4); Chlr: commercialChlorhydrol; −12 and −24 stand for the amount of Al supplied per gmineral, respectively, 12 and 24 mmol Al g⁻¹ clay.

Calcination in mufle oven (heating rate: 12-13° C. min⁻¹).

Note: Trials using at step 3 acetic and hydrochloric acid in place ofoxalic or citric acid gave as well pillared micas with c.a. 18 Åspacings (samples calcined at 500° C.). At the difference with samplestreated with the preferred acids, the X-ray pattern exhibited a secondreflection at 14 Å (room temperature drying) which was more significantthan in samples using oxalic or citric acid, but less important thanwhen step 3 was omitted.

The intensity ratios of the 18 Å phase to the 14 Å phase in samplestreated with acetic acid, hydrochloric acid, and when omitting step 3 insamples dried at room temperature were, respectively, 3.6, 3.1 and 2.0,and increased to 16, 15 and 9 respectively after calcination at 500° C.,thus showing that acetic acid and hydrochloric acid may also be used atstep 3.

2. Al-Pillaring of Vermiculites

Venmiculites from Palabora Company (South Africa) and Libby (Montana)deposit were treated following the “standard method” and characterised.

Starting Vermiculites

The vermiculite from Palabora Company was superfine grade and it isnoted as P_(i). The vermiculite from Libby (Montana) deposit is noted asL_(i).

The C.E.C. determined on Ba-exchanged P_(i) was 1.85 meq g⁻¹

The chemical analyses obtained by I.C.P.S. for P_(i) and L_(i) are givenin Table 7 (in wt %):

TABLE 7 Chemical analysis data (wt %) on basis of samples calcined at1000° C. SiO₂ Al₂O₃ Fe₂O₃ MgO CaO K₂O F⁻ L.I. P_(i) 43.3 9.3 8.6 24.15.1 4.8 0.9 11.1 L_(i) 41.2 9.2 6.8 28.3 3.3 4.6 0.2 12.6 L.I.: weightloss on ignition at 1000° C.

Pillared vermiculites were prepared according to the sequence oftreatments described for the mica. Palabora and Libby vermiculites willbe distinguished by, respectively, P (P₁ to P₅) and L (L₁ to L₅). Theexperimental conditions employed at the various steps are indicatedhereafter.

Conditioning and pillaring conditions

Step 1: Nitric acid conc. (M) 0.78 for P_(i) and 0.62 for L_(i) Duration(h)  4 Temperature (° C.) 95 Concentration of solids (wt %) 10

Samples P₁ and L₁

Step 2: Calcination at 600-650° C. 4 h

Samples P₂ and L₂

Step 3: oxalic acid conc. (M) 0.12 Duration (h) 1 Temperature (° C.) 80Concentration of solids (wt %) 10

Samples P₃ and L₃

Step 4: NaCl solution conc. (M) 3 Number of renewals 5 × 12 hTemperature (° C.) 95  Concentration of solids (wt %) 5

Samples P₄ and L₄

Step 5: Pillaring solution OH/Al = 2.4 mmol Al/g solid 24 contact time(h) 4 temperature (° C.) 80

Samples P₅ and L₅

Characteizadon of Conditioning Intermediates (P_(i) to P₄, L_(i) to L₄)

X-ray Diffraction Data

The spacings of the samples dried at room temperature and calcined at500° C. at the different steps are given in Table 8.

TABLE 8 Basal spacings (in Å) of samples dried at room temperature andcalcined at 500° C. Sample Room T (Å) 500° C. (Å) P_(i) 24.5, 14.2,12.4, 11.8 25, 14, 11.5, 9.9 P₁ 24.7, 11.9 9.8 P₂ 9.8-10.0 P₃ 9.8-10.259.9 P₄ 12.2-12.4 9.7-9.65, (12.2)* L_(i) 25, 12.6, 12.0 24.9, 12, 10.15L₁ 25, 12.0 9.8 L₂ 10.0 L₃ 10.0-10.2 10.0-10.2 L₄ 12.2-12.4, (13.6)9.7-9.65, (12.2)* *partial rehydration

The Na-exchange (P₄, L₄) was confirmed by the spacing of 12.2 Å at roomtemperature (hydrated form) collapsing to 9.65-9.7 Å after heating at500° C.

Textural Characteristics

The Na-exchanged samples (P₄, L₄) outgassed at 200° C. for 6 h (Table 9)show no microporosity, and an increment of the surface area and of thetotal pore volume with respect to the starting vermiculite (P_(i)). Thenitrogen sorption isotherms corresponding to P₁ and P₄ are shown in FIG.3.

TABLE 9 Textural characteristics Specific surface area (S_(BET)), totalpore volume (V₀) and micropore volume (V_(μ)) (t-plot method) of samplesprecalcined at 500° C. S_(BET) V₀ V_(μ) Sample (m²g⁻¹) (cm³ g⁻¹) (cm³g⁻¹) P_(i) 2 0.004 0.000 P₄ 43 0.074 0.001 L₄ 22 0.036 0.000

Particle Size Analysis

The analysis data of sample P4 are compared with those of the startingvermiculite in Table 10. As in the case of micas, a reduction of theparticle size occurs during the conditioning steps.

TABLE 10 Particle size analysis (0.1 μm-900 μm) Size (μm) Size (μm) Size(μm) Sample 90%< 50%< 10%< P_(i) (superfine) 819 515 22 L_(i) 684 290 74P₄ 252 102 32

Other Characteristics

The CEC (cation exchange capacity) prior to pillaring (P₄) was 1.32 meqg⁻¹ (micro-Kjeldahl method on ammonium-exchanged form). Note: Thestarting vermiculites (P_(i), L_(i)) may be directly converted in anydesired homoionic form without proceeding to steps 1 to 3. However,pillaring cannot be achieved without these steps.

Characterization of Al-pillared Vermiculites

Textural and Structural Characteristics

The textural results derived from the nitrogen sorption isotherms ofsample P5 (uncalcined and previously calcined at different temperatureswith heating rate of 1° C. min⁻¹) are given in Table 11. Prior to thesorption measurements, the samples were outgassed at 200 ° C. for 6 h.

TABLE 11 Textural characteristics. BET specific surafce area (S_(BET)),total pore volume (V₀) and micropore volume (V_(μ)) of samples calcinedat increasing temperatures S_(BET) V₀ V_(μ)* Sample (m²g⁻¹) (cm³ g⁻¹)(cm³ g⁻¹) P5-200 (Na) 296 0.185 0.098 P5-400 (Na) 307 0.192 0.109 P5-500(Na) 322 0.215 0.120 P5-600 (Na) 241 0.166 0.071 P5-700 (Na) 216 0.1440.068 P5-400 (Ca) 291 0.197 0.112 P5-500 (Ca) 318 0.211 0.119 P5-600(Ca) 326 0.215 0.123 P5-700 (Ca) 226 0.159 0.082 P5-800 (Ca) 184 0.1380.062 L5-400 (Ca) 241 0.158 0.083 L5-600 (Na) 212 0.142 0.071 *Method of[reference 17]

The textural characteristics obtained on Palabora vermiculite,exchanged, at step 4, with a calcium salt instead of a sodium salt, bothhomoionic forms being pillared as indicated above, are compared in Table11. The use of a Ca salt at the step 4 improves the characteristics ofthe pillared material at similar calcination temperatures.

The complete nitrogen adsorption-desorption isotherms of P5 calcined at400° C. and 700° C. are shown as example in FIG. 3

As seen in Table 12, after treatment with the pillaring solution, theintercalation of the Al₁₃ is confirned by the expansion of theinterlayer distance to 18.7-18.2 Å. A minor fraction of the vermiculitewas intercalated with smaller aluminium species (mainly monomericaluminium) with spacings of 14.1-13.7 Å. At 400° C., the spacing wassomewhat reduced (18.4 Å) and the minoritary fraction intercalated withmonomeric species collapsed to 10.5 Å. No significant difference wasnoticed according to the cation species exchanged at step 4.

FIG. 4 shows the XRD diffraction patterns of the Al-intercalatedPalabora vermiculite, aflter drying at 60° C. and subsequent calcinationat increasing temperatures (in the same conditions as above).

TABLE 12 Basal spacing d001 (Å) of pillared vermiculites (Samplescalcined at heating rate of 1° C./min; plateau maintained for 2 h). T (°C.) 60 400 500 600 700 800 P5 (Na) 18.7 18.4 18.2-17.7 17.2 16.4 16.3 P5(Ca) 18.7 18.2 17.7 17.2 16.7 16.0 L5 (Na) 18.7 18.2 17.8 17.5 16.6 —

3. Al-Pillaring of Precalcined Vermiculites

Starting Vermiculite

Exfoliation of vermiculite is done by feeding crude vermiculite atcontrolled rate in a vertical furnace heated at 800-1000° C. Theresidence time is of the order of a few seconds, during which thehydration water around the charge balancing cation (Mg²⁺) isinstantaneously vaporized. Due to high local steam pressure in theinterlayers, flash expansion of the vermiculite platelets occurs, with aten- to twenty-fold expansion of the platelets, resulting in low densitymultilayer particles. These exfoliated vermiculites are employed e.g.for their thermal insulating properties. Separation of the fines is donee.g. by cyclonisation. These fines are not recycled (wastes).

The fine fraction of Palabora vermiculite with mean particle size of 50μm recovered after the cyclonisation step will be referred to hereafteras “precalcined vermiculite” (previously named ‘wastes’). Small amountsof calcite and possibly biotite were identified by X-ray diffraction.The experiments were done on the as received sample, without grindingand fractionation treatments.

The cation exchange capacity (CEC) of the starting sample was 0.48 meqg⁻¹, namely, about three times less than normal value found for crudetrioctahedral vermiculites (example II). This low value is probablyrelated to the previous flash treatment at 800° C. The startingvermiculite will be noted as V_(i).

Conditioning of the Precalcined Vermiculite

Conditioning consisted of submitting the starting vermiculite to asimilar sequence of treatments (standard method) as that for micas andcrude (uncalcined) vermiculites. The conditions were as follows:

Step 1:

The starting vermiculite was treated with a 0.23 M solution of nitricacid at 95° C. for 4 h and under continuous stirring, using 25 ml of theacid solution per gram of vermiculite. The acid-leached solid wasthoroughly washed and dried at 60° C. (Sample V₁ hereinafter).

Step 2

Solid V₁ was calcined at 600° C. for 4 h under static air (sample V₂).

Step 3

Sample V₂ was leached for 4 h at 80° C. under continuous stirring with a0.5 M citric acid solution (pH=2.1) using 40 ml g⁻¹ of solid. The solidwas washed free from excess acid and salts, and dried at 60° C. (sampleV₃).

Step 4

Solid V₃ was treated 5 times (for 12 h each) with a 1 M sodium chloridesolution (50 ml g⁻¹ of solid). The exchange operation was preferablycarried out at 95° C. under continuous stirring. The solid recovered waswashed and dried at 60° C. (sample V₄).

At the end of this four steps treatment, the Na-exchanged vermiculitewas ready for the pillaring operation. Note that at step 4, theNa-vermiculite may be converted via any usual exchange method to anydesired cationic form.

Al-pillaring of Precalcined Vermiculite

The Na-exchanged vermiculite obtained at the end of step 4 (sample V₄)was dispersed in water (0.5 wt % of solid) and the suspension wasstirred for 24 h (unnecessary in a continuous procedure). TheAl-pillaring solution (base hydrolyzed AlCl₃, with OH/Al molar ratio of2.4) was slowly added under stirring to the vermiculite dispersion,adding a sufficient volume to supply 12 mmol Al g⁻¹ vermiculite.

After addition of the pillaring solution, the final suspension was agedfor 4 h at 80° C. under stiring. The suspension was centrifuged and thesolid was washed and dried at 60° C. (sample noted V₅). The dried samplewas then calcined for two hours at 500 and 700° C., using a heating rateof 13° C./min.

Characterization of Intermediates (Samples V₁ to V₄)

The solids obtained at each separate step were characterised with thesame techniques and methods as for the preceding examples. As mentionedearlier (in examples I and II), in the continuous preparation process,namely, from the starting vermiculite (V_(i)) to its Al-pillared form(V₅), intermediate dryings are omitted.

The main observations concerning the solids obtained at the end of steps1 to 4 are summarised hereafter. The characterisation of the Al-pillaredvermiculite (V₅) will be treated separately.

X-ray Diffraction

The basal spacings of samples (previously calcined for 2 h at 500 ° C.)obtained at the end of steps 1 to 4 are given in Table 13.

TABLE 13 Basal spacings (in Å) at 500° C. V_(i) 10.15 V₁ 10.1 V₂ 10.1(600° C.) V₃ 10.15 V₄  9.7 (12.1)

The diffraction pattern of the starting vermiculite (V_(i)) exhibitedreflections of hydrated vermiculite (peak at 14.5 Å), biotite (10.1 Å)and interstratified, R=1, biotite-venniculite with interplanar distancesof 25.2 and 12.2 Å.

After acid leaching and calcination at 500° C. (V₁-500), theinterstratified phase disappeared and a single reflection at 10.1 Å witha much increased intensity was noticed.

The X-ray patterns of the samples V₂ (thermal treatment) and V₃ (citricacid leaching) did not exhibit significant modification with respect tothat of calcined V₁.

A small but qualitatively important decrease of the basal spacing wasnoticed for the Na-exchanged vermiculite (V₄-500), with a contraction of0.3-0.4 Å, indicative of total exchange. Partially Na-exchanged samplesexhibited, after calcination at 500° C., peaks corresponding tointerplanar distances of 10.1 and 9.9 Å.

As it will be illustrated below, well pillared vermiculites were onlyobtained from thoroughly exchanged Na-vermiculite, as for the precedingexamples.

Cation Exchange Capacity

After treatment with nitric acid (sample V₁) the cation exchangecapacity increased from 0.48 (V_(i)) to 1.49-1.50 meq g⁻¹. Treatingvermiculite in step 1 with nitric acid (0.23 M at 95° C. for 4 h) orcitric acid (0.5 M at 80° C. for 4 h) gave solids with identical CECs.

After calcination at 600° C. (sample V₂), the CEC decreased from 1.50 to1.11 meq g⁻¹ (a loss of about 26%).

Removal of the interlayer species upon treatment with citric acid(sample V₃) resulted in an increase of the CEC, from 1.11 to 1.23 meqg⁻¹. The initial value of 1.50 meq g⁻¹ was not restored, which indicatesa reduction of the overall negative charge.

Textural Properties

The nitrogen adsorption-desorption isotherms at 77K of the starting(V_(i)-500) and Na-exchanged vermiculites (V₄-500), shown in FIG. 5,correspond to type IV of the IUPAC classification, characteristic ofmesoporous solids, with a H3-type hysteresis loop, generally encounteredfor (layered) lamellar minerals [reference 18].

The textural characteristics of samples V_(i) to V₄ are indicated inTable 14.

TABLE 14 Textural parameters of selected samples S_(BET) V_(μ) V₀ Sample(m²g⁻¹) (cm³ g⁻¹) (cm³ g⁻¹) V_(i) 11 0.000 0.031 V₁ 68 0.008 0.097 V₂ 200.001 0.057 V_(2-Na) 17 0.001 0.050 V₄ 30 0.001 0.086 V_(5′)-500 1530.056* 0.121 V₅-500 192 0.066* 0.177 V₅-500 179 0.065* 0.150 V₅-700 1210.041* 0.118 *method of [reference 17]

As shown in Table 14, the treatment with nitric acid enhances theexternal surface area, from 11 m² g⁻¹ (untreated vermiculite, V_(i)) to68 m² g⁻¹ (V₁) mainly attributable to the increase of the macroporevolume. Micropores are almost absent.

The thermal treatment (sample V₂) provoked a diminution of the specificsurface area, from 68 to 20 m² g⁻¹.

The nitrogen sorption isotherms established on samples V₂ (not shown)and V₄ did not exhibit marked differences. The specific surface area ofthe vermiculite subsequently leached with citric acid (step 3) andNa-exchanged (step 4) was 30 m² g⁻¹ (V₄ in Table 14), thus only slightlyhigher.

Characterization of Al-pillared Precalcined Vermiculites

X-ray Diffraction Analysis

The pillaring step is of course the one which leads to the obtention ofpillared vermiculite and, according to whether a 18 Å phase (at roomtemperature) is achieved or not, it constitutes somehow an ‘enlightener’on whether the intermediate steps were or were not properly conducted.

FIG. 6 shows the XRD patterns of V₅ after calcination between 500 ° C.and 700° C. The basal spacings of selected samples after calcination aregiven in Table 15.

TABLE 15 Basal spacings (in Å) Sample Spacing (Å) V_(5′)-500 (withoutstep 3) 17.6-17.7 V₅-500 17.6-17.7 V₅-600 16.4 V₅-700 16.3

Al-pillared vermiculite exhibited a basal spacing of 18.6 Å for sampledried at room temperature, and 17.6 Å after calcination at 500° C.(Table 15). Similar spacings were found for Al-pillared micas andAl-pillared crude vermiculite.

Pillared and Al-exchanged phases can be easily distinguished on the XRDpatterns. In order to evaluate the quality of the pillared materials,the ratio between the peak height of the 001 reflection of the pillaredphase (ca. 17.6 Å at 500 ° C.) and that of the peak corresponding to theAl-exchanged vermiculite (peak at 10.5 Å at 500° C.), in short asI₁₈/I₁₀, is used, after background subtraction. For instance, there wasa substantial increase of the peak intensity ratio (I₁₈/I₁₀) when thematerial obtained at the end of step 2 was treated with citric acid(I₁₈/I₁₀=7-11) compared with a sample which was not treated(I₁₈/I₁₀=3.1).

Thermal Stability

Pillared vermiculite calcined at 500° C. had a spacing of 17.6-17.5 Å(Table 15) which decreased to 16.4 and 16.3 Å after calcination at 600and 700° C. respectively. The decreasing interplanar distances aresimilar to those observed for pillared micas.

Thermogravimetry (TGA, DTG)

The pillaring of vermiculite was confirmed by TGA data. The Al-pillaredV₅ sample showed between 60 and 300° C., a weight loss about twice asmuch as for V₄ (Na-vermiculite). The further loss of the OH ligands ofthe pillars was indicated by a DTG minimum at 515° C. The structuraldehydroxylation of the vermiculite occurred at 835° C. The total weightloss between 60 and 1050° C. of the Al-pillared vermiculite amounted to16.42%, compared with 7.1 and 9.46% for, respectively, V_(i) and V₄.

Textural Characteristics

N₂ adsorption-desoiption isotherms were established on pillared samplesbefore and after calcination at 500° C. As in the case of pillaredsmectites (PILCs) and pillared micas (PILMs), intercalation of Alpillars between the layers is accompanied by the development ofmicroporosity.

As seen in Table 14, the BET surface area of samples calcined at 500° C.increased from 30 m² g⁻¹ before pillaring (sample V₄) to 179-192 m² g⁻¹for a sample which was previously treated with citric acid (V₅′-500), orto 153 m² g⁻¹ when the citric acid leaching (step 3) was omitted(V₅′-500). This increase of the surface area is directly related to thedevelopment of microporosity.

Residual CEC and Acid Content

The residual CEC (V₅-500) obtained for a pillared vermiculite was 0.27meq g⁻¹. A value of 0.29 meq g⁻¹ was obtained for Al-pillared micas.

The acid content (temperature-programmed desorption of ammonia between100 and 550° C.) gave an average value of 0.20 mmol g⁻¹.

MAS-NMR Spectroscopy

The ²⁷Al MAS-NMR spectrum of V₄ showed only one signal at 63 ppmcorresponding to structural tetrahedral aluminium (aluminium in thetetrahedral layers). The Al-pillared sample (V₅-500) exhibited twosignals at 3-5 ppm, typical for octahedral Al, and at 63 ppm,characteristic of tetrahedral Al. The signal near 5 ppm corresponds toAl^(VI) (octahedral Al) of the pillars and the one at 63 ppm is thesuperimposition of the signal of Al^(IV) (tetrahedral Al) of the pillarsand Al in the tetrahedral layers of vermiculite.

Alternative Conditioning Treatments Investigated

In order to have a better insight into the role of each one of thedifferent steps of the standard method, several alternatives have beenexamined. To check the effect of those variables on pillaring, XRD isthe most adequate technique because it permits to identify the phases inpresence and give an evaluation of their relative proportions.

Successful pillaring is evidenced by the absence of unpillared fraction(X-ray diffraction peak at 10.1 Å after calcination of the sample at500° C.) after the pillaring treatment. Intercalation of Al₁₃-typespecies should be favoured with respect to exchange with monomericaluminium. The I₁₈/I₁₀ ratio, as defined above, ranged between 0.5, forvery poorly pillared vermiculites, and 7 and higher for well pillaredmaterials in the case of precalcined vermiculite.

Some results of additional trials investigated (summarized in Table 16)are briefly described hereafter and commented altogether. Step 3 (citricacid treatment) when not specifically targeted has been omitted becauseit was not indispensable to verify suitable pillaring of the material.In doing so, a more rapid information on the influence of the modifiedparameters can be obtained. However, better pillared materials areobtained when carrying out step 3.

TABLE 16 Main alternatives investigated. Trial Step 1 Step 2 Step 3 Step4 n1 HNO₃ 0.17M //////// HNO₃ 0.25M //////// HNO₃ 0.46M //////// n2citric //////// n3 HCl //////// n4 /////////// //////// n5 HNO₃ H₂Osteam ------------ n6 HNO₃ //////// //////// n7 HNO₃ //////// n8 HNO₃//////// HNO₃ NH₄ ⁺ //////// means step not performed

Trials related with step 1. Effect of acid concentration

Run 1.

In distinct experiments, acid treatment in step 1 has been performedwith, respectively, 0.17 [0.006 mole H⁺g⁻¹], 0.25 [0.009 mole H⁺g⁻¹],and 0.46 [0.016 mole H⁺g⁻¹] M nitric acid solutions, keeping constantthe solid concentration (thus changing the mol H⁺g⁻¹ solid ratio), theleaching temperature and duration of the treatment being as in the“standard” procedure, and steps 2, 4, and 5 being subsequently carriedout according to the standard procedure.

Pillaring was better achieved when vermiculite was treated with 0.009mole nitric acid per gram solid. Using either higher or lower acidconcentration resulted in poorer pillared materials. The best resultswere obtained when vermiculite was treated with a quantity of acid ofabout five to six times the CEC of the vermiculite; higher acidconcentrations provoked irreversible structural damage, resulting innonpillarable materials.

Influence of Type of Acid (Runs 2 and 3)

Run 2.

Substituting citric acid for nitric acid in step 1, in other wordscarrying out step 3 instead of step 1, followed by steps 2, 4 and 5,resulted in very poorly pillared material (I₁₈/I₁₀ ratio=0.6),suggesting that steps 2 to 5 did not operate as in the “standard”procedure.

Run 3.

Substitution of hydrochloric acid or sulfuric acid for nitric acid withsimilar concentration (steps 2, 4 and 5 being carried out as in the“standard” procedure) provided a pillared material in the case ofvermiculite (I₁₈/I₁₀=6.0). For the mica, a very small fraction waspillared.

Run 4.

Experiments in which vermiculite was directly leached with citric acidfollowed (after washing the solid) by Na-exchange (step 4) andAl-pillaring (step 5), thus omitting steps 1 and 2 led to partialpillaring, in spite of the fact that the CEC of the Na-exchangedmaterial obtained at step 4 was 1.49 meq g⁻¹ (1.50 meq g⁻¹ when treatedwith nitric acid). The I₁₈/I₁₀ ratio was 1.2 (1.1 in a duplicate trial).This result indicates that freeing the exchange positions of thestarting vermiculite and converting it to a homoionic form are notsufficient to ensure adequate pillaring (adequate pillaring meaning thata predominant fraction of the sample is pillared).

Run 6.

Carrying out steps 1, 4 and 5 following the standard conditions (steps 2and 3 omitted) resulted in the nearly total absence of pillaring. TheI₁₈/I₁₀ peak ratio was only 0.46. This confirms that step 2 isindispensable to the obtention of a well-pillared vermiculite.

Trials Related to Step 3 (Complexing Agent)

Run 7.

Pillared vermiculite with acceptable characteristics (spacing, surfacearea and micropore volume) could be obtained when the citric acidtreatment was suppressed. However, carrying out this treatment resultedin a significant improvement of the characteristics of the pillaredmaterial. Using oxalic acid had a similar beneficial effect, whereas noimprovement was noticed when using nitric acid instead of citric oroxalic acid in step 3. Other complexing agents (f.i. acetylacetone) wereless efficient or needed longer contact times than complexing acids.

Trials Related to Step 4 (Na-exchange)

Run 8.

Attempts to suppress step 4 (sodium exchange) or to pillarammonium-exchanged vermiculite were unsuccessful; no pillaring at allwas observed. However, using calcium instead of sodium provided wellpillared materials with slightly higher micropore volumes and improvedresistance of the specific surface area to thermal treatment (compareP5-600 (Na) rand P5-600 (Ca) of Table 11). Exchange with hydratedcations is thus of crucial importance to the obtention of well pillaredvermiculites (as well as for micas) and, in particular, the degree ofcompletion of the exchange. Indeed, a clear relation exists between thedegree of exchange and the fraction of pillared vermiculite.

Application Areas of Pillared Micas and Vermiculites

Pillared micas and vermiculites may be used as catalysts, as such and/orin adjunction with other catalytic components, for the followingreactions: cracking-hydrocracking, isomerisation-hydroisomerisation,dewaxing, alkylation and dealkylation,disproportionation-transalkylation, upgrading of light cycle oils,oligomerisation of olefins, dehydration of alcohols, hydration ofolefins, ether formation, hydroxylation of phenols and derivatives,condensation reactions, methanol to hydrocarbons, bydroformylation,synthesis of glycols, CO hydrogenation, Fischer-Tropsch, synthesis gas,HDS, HDN, HDM, NO reduction, deep oxidation, photocatalysis.

Pillared micas and vermiculites may find application as adsorbents; ingas separation, as scavenger for heavy metals (treatment of wastewaters); SO₂, NO_(X) abatement; in cation-selective composite membranes,as solid electrolytes; host material for (conducting) polymers; as hostmaterial for dispersed nitrides, oxynitrides, carbides, perovskites;modified electrodes.

In particular, the pillared micas and vermiculites obtained according tothe present invention may be used in any combination with othercatalytic systems as, f.i. zeolites, oxides and mixed oxides. They mayalso be used as a support to metals, metal oxides and metal compounds.

Chemical treatment(s) aiming to modify the surface properties of thepillared micas and vermiculites, such as treating with, e.g. phosphorus-and sulphur-containing compounds, are within the scope of thisinvention.

Catalytic Examples

Hydroconversion of Paraffins

Hydroisomerization of octane was conducted in the vapour phase onPt-impregnated samples (1 wt % Pt) of Al-pillared vermiculites and micasand on a commercial zeolite Beta (ZB25 from P.Q. Zeolites) as areference. Impregnation and activation were similar to those reported in[reference 19].

Total flow of octane-/hydrogen mixture was 10 ml min-1, WHSV: 0.92 h-1,H2/C8:15.6. Reaction was made in temperature-programmed mode (0.2° C.min-1) between 150 and 400° C. On-line analysis of the reaction productswas done in a gaschromatograph equipped with flame ionisation detectorand CPSil-5 capillary column. The results obtained over the zeolite beta(ZB25) and different samples of pillared micas (symbolized by F) andvermiculites (S) are shown in FIGS. 7 and 8, where the variation oftotal conversion, of the yields of isomers and of the cracked productsare plotted against reaction temperature. Higher yields of C8 isomersare produced over the pillared micas and vermiculites compared with thereference catalyst, with, at maximum isomerisation conversion, yields of80% for the pillared micas and vermiculites compared with 70% for theH-Beta zeolite, and selectivities to C8 isomers between 89.6 and 92.4%vs 86.2 for the zeolite.

For sake of comparison, results obtained at maximum isomerisationonversion on US-Y zeolites (commercial samples CBV400 to CBV780, from PQZeolite), H-Beta (ZB25 and ZB75 from PQ Zeolite), Al-pillared saponite(Al(ACH)PSY, a pilor scale prepared sample with Al-chlorhydrol), and onAl-pillared micas (samples F) and Al-pillared vermiculites (samples S),all loaded with 1 w t% Pt and tested in similar conditions are compiledin Table 17. Sample 3S044 in this table is an Al-pillared vermiculitethat was treated with diluted hydrochloric acid after being calcined at500° C. (referred to as stabilized pillared vermiculite), together withthose obtained on ZB25 (H-beta zeolite), Al pillared saponite(Al(ACH)PSY) and non stabilized Al-pillared vermiculite (1S044). Thecorresponding curves are shown in FIG. 9. Higher performances(conversion, yield of isomers and selectivities) were obtained for thepillared materials of the invention. In particular, the activity of thestabilized sample was significantly improved compared with nonstabilized counterparts.

TABLE 17 Results obtained at maximum isomerization conversion over somezeolites, an Al-pillared saponite (AlP-S), and over Al-pillared micas(samples F) and Al-pillared vermiculites (samples S). Catalyst T maxTotal Yiso Sel. Si/Al iso conv i-C8 Ycr i-C8 Mono-iso Di-iso 2MC7/ 1% Pt(° C.) (%) (%) (%) (%) (%) (%) /3M C7 CBV 2.6 246 76.5 62.7 13.9 81.969.6 30.4 0.86 CBV 2.6 182 68.3 51.8 16.5 75.8 68.4 31.6 0.91 CVB 2.8215 80.5 63.7 16.6 79.1 65.5 34.5 0.83 CVB 13.0 220 83.4 66.9 16.6 80.262.2 37.8 0.84 CVB 21.0 267 79.8 67.2 12.7 84.1 66.2 33.8 0.82 CVB 30.0270 76.7 61.5 16.2 78.9 72.2 27.8 0.82 CVB 37.1 269 80.2 67.1 13.1 83.768.1 31.9 0.81 ZB-75 37.5 212 79.2 68.3 10.9 86.3 68.2 31.8 0.89 ZB-2513.2 194 84.7 71.0 13.7 83.8 61.5 38.5 0.88 AlP-S 244 83.7 67.8 16.081.0 66.2 33.8 0.85 1F029 242 87.9 78.7 9.2 89.6 62.3 37.7 0.85 6F010238 85.6 79.1 6.5 92.4 64.1 36.0 0.86 1F041 241 86.4 79.1 7.4 91.5 63.836.2 0.85 2F045 238 88.0 80.0 7.9 91.0 65.8 34.2 0.85 2F047 246 83.676.8 6.9 91.8 65.8 34.2 0.85 1S044 241 87.8 78.9 8.9 89.9 62.3 37.7 0.853S037 222 86.9 80.2 6.7 92.3 62.4 37.6 0.88 3S044* 207 89.5 83.3 6.293.1 59.7 40.3 0.90 *stabilized

A duration test was performed over a stabilized Pt-impregnated (0.5 wt %Pt) Al-pillared mica at 207° C. and WHSV of 0.92 h⁻¹. After 190 h timeon stream, no deactivation was noticed, with a total average conversionof 88.2% and yield of C8 isomers of 82.8% (selectivity of 93.9%).

Reduction of NO by NH₃

A sample of pillared mica and a commercial zeolite ZSM-5 (SM-27,Si/Al=12-13.5, from VAW Aluminium AG) were twice Cu-exchanged with 2 Msolution of copper nitrate at 80° C. for 1 h, and removal of excesssalt. The catalytic tests were carried out in a fixed-bed microreactoron 50 mg samples diluted in small-sized quartz. The catalysts wereheated at 90° C. for 2 h in flowing dry air. The reaction conditionswere as follows: total flow: 200 ml min⁻¹ (40 ml min⁻¹ of NO, 5.000 ppmin He; 56 ml min⁻¹ NH₃, 5.000 ppm in He; and air=104 ml min⁻¹ (10.5% O₂vol/vol). WHSV was 0.18 g NO g cata⁻¹ h⁻¹. On-line gas phase analysiswas done in a Rotork Chemiluminescence NOx Analyzer. The experimentalvalues were taken at stabilized conversions. The comparative results areshown in FIG. 10. Both Cu-ZSM-5 and Cu—Al-pillared mica (M5) exhibitedsimilar performances, total reduction of NO being attained at about 200°C. in the zeolite and at above 300° C. for the Cu-exchanged Al-pillaredmica.

REFERENCES

1. Rich, C. I., Soil Sci. Soc. Am. Proc. 24,26, 1960.

2. Hsu, P. H. and Bates, T. F., Soil Sci. Soc. Am. Proc. 28, 763, 1964.

3. Brydon, J. E. and Tumer, R. C., Clays Clay Miner. 20, 1, 1977.

4. Barnishel, R. I., in Minerals in Soil Environments, Soil Sci. Soc.Amer., Madison, p.331, 1977.

5. Schutz, A. and Poncelet, G., unpublished results

6. Hsu, P. H., Clays Clay Miner. 40, 300, 1992.

7. d'Espinose de la Caillerie, J. B. and Fripiat, J. J., Clay Miner. 29,133, 1994.

8. Michot, L. J. et al., Clay Miner. 29, 133, 1994.

9. Vaughan, D. E. W., and Lussier, R. J., Proc. 5th Zeolite Conf., L. V.Rees (Ed.), Heyden & Sons, 94, 1980.

10. Akitt, J. W. et al., J. Chem. Soc., Dalton Trans. 604, 1972

11. Bottero, J. Y. et al., J. Phys. Chem. 84, 2933, 1980

12. Lahav, N. et al., Clays Clay Miner. 26, 107, 1978.

13. Schutz, A. et al., J., Clays Clay Miner. 35, 251, 1987.

14. Zhonghua, G. et al., Microporous Mater., 3, 165, 1994.

15. Bergaoui, L. et al., Chem. Soc. Faraday Trans. 91, 2229, 1995.

16. de Boer, J. H. and Broekhoff, J. C. P., J. Catal. 10, 391, 1968.

17. Remy, M. J. et al., Microporous Mater. 7(6), 287, 1996.

18. Sing, K. S. W. et al., Pure Appl. Chem. 57, 603, 1985.

19. Moreno, S. et al., J. Cattil. 162, 198, 1996.

What is claimed is:
 1. A process for preparing pillared trioctahedralmicas and/or vermiculites having a layer charge, said processcomprising: conditioning the micas and/or vermiculites throughaccelerated weathering so as to partially reduce the layer charge of themicas and/or vermiculites, thereby forming charge-reduced micas and/orvermiculites, wherein conditioning the micas and/or vermiculitescomprises successive steps as follows: a) treating the micas and/orvermiculites with a solution of an acid; b) calcining the productrecovered from step a) at about 600° C. for approximately 4 hours understatic air; and c) treating the product from step b) with a solution ofa salt of a hydrated cation until exchange is completed; and pillaringthe charge-reduced micas and/or vermiculites.
 2. A process according toclaim 1, wherein the charge-reduced micas and/or vermiculites areconverted into homoionic forms of a hydrated cation prior to thepillaring operation.
 3. A process according to claim 1, wherein the acidof step (a) is nitric acid.
 4. A process according to claim 1, whereinthe product of step (b) is leached with a diluted inorganic or organicacid prior to step (c).
 5. A process according to claim 4, wherein thediluted inorganic or organic acid is a complexing acid.
 6. A processaccording to claim 5, wherein the complexing acid is oxalic acid orcitric acid.
 7. A process according to claim 1, wherein the pillaringoperation is performed by adding a pillaring solution containing apillaring species to a dispersion of trioctahedral micas and/orvermiculites or by adding a dispersion of trioctahedral micas and/orvermiculites to a pillaring solution containing the pillaring species.8. A process according to claim 1, wherein the pillaring operation isperformed by adding a pillaring solution comprising pillaring speciesselected from the group consisting of Al, Zr, Ti, Si, Cr, Fe, Ta, Nb, Gaand combinations thereof, including lanthanides.
 9. A process accordingto claim 1, wherein the pillaring operation is performed by adding apillaring solution comprising a base hydrolysed Al solution as pillaringspecies.
 10. A process according to claim 1, wherein the pillaringoperation is performed by adding a based hydrolysed Al solutioncontaining Al hydroxy-polymer Keggin-like cations with general formulaAlO₄Al₁₂(OH)₂₄(H₂O)₁₂ ⁷⁺.
 11. A process according to claim 1, whereinthe vermiculite which is used has been calcined prior to theconditioning and pillaring operation.
 12. A process according to claim1, wherein said pillaring operation is followed by an ionicpost-exchange.
 13. A process according to claim 12, wherein said ionicpost exchange is with Cu ions.
 14. Pillared vermiculites precalcined ornot obtained according to claim 1, wherein the pillared vermiculitesexhibit basal spacing above 16 Å, and exhibiting surface areas of 184 to326 m² g⁻¹, micropore volumes of 0.062 to 0.123 ml g⁻¹ and a total porevolume of 0.138 to 0.215 ml g⁻¹.